The present invention relates to a method and apparatus for surface treatment and deposition of coatings on a conductive material. More particularly, the present invention relates to such methods and apparatus that use corona discharge for applying a diffuse coating to the surface, and still more particularly to a cable for use in such methods and apparatus.
It is desirable to apply coatings to a surface of a conductive material to cause the material to have improved characteristics. For example, it is known to apply a diffused titanium carbide layer to a surface of steel to provide surface hardening of the steel. One method of achieving such coating involves the use of a glow discharge as a processing plasma, with the discharge being established and sustained using radio frequency (rf) power. Ion nitriding of titanium diffusion layers using a plasma assisted treatment typically occurs when the specimen to be coated is located in a vacuum chamber. For further information regarding surface treatment using plasma resulting from a glow discharge, reference may be made to, e.g., Wierzchon et al., "Formation and Properties of Titanium Carbide Layers Produced on Steels Under Glow Discharge Conditions," Institute of Materials Science and Engineering, Warsaw Technical University, Poland (1989); Talivaldis Spalvins, "Advances and Directions of Ion Nitriding/Carburizing", NASA Technical Memorandum 102398, September 1989; S. Veprek, "Preparation of Inorganic Materials, Surface Treatment, and Etching in Low Pressure Plasmas: Present Status and Future Trends", Plasma Chemistry and Plasma Processing , Vol. 9, No. 1, 1989 (Supplement); and U.S Pat. No. 4,894,256 to Gartner et al.
Additional patents known to applicants that provide background information relative to surface treatment using plasma resulting from a corona or glow discharge are as indicated below.
U.S. Pat. No. 4,940,521 to Dinter et a1. discloses apparatus for treating the surface of electrically conducting materials such as metal foil or plastic film containing conductive particles, by means of electrical corona discharge. The electrodes, which are covered by dielectric material, extend horizontally and are spaced from the surface to be treated. A housing encloses the electrodes and is connected to receive atomized liquid.
U.S. Pat. No. 4,940,894 to Morters is directed to an electrode for a corona discharge apparatus. The electrode includes a steel tube with a dielectric covering.
U.S. Pat. No. 4,879,100 to Tsutsui et al. and "Plasma Surface Treatment of Polypropylene-Containing Plastics", Koichi Tsutsui et al., Journal of Coatings Technology, Vol. 61, No. 776, September 1989, are directed to corona discharge treatment apparatus for treating the surface of, for example, a plastic automobile bumper. The apparatus shown in the patent includes an electrode wire fitting member with a large number of electrode wires dependent therefrom for contacting the upper surface of the object to be treated. In FIG. 1a, the equipment is shown including a base electrode, which may be grounded and which is shaped to conform to the inside surface of the object to be treated.
U.S. Pat. No. 2,969,463 to McDonald shows apparatus for treating the surfaces of a plastic sheet. One of the fixed electrode assemblies, as shown in FIG. 3, is disposed spaced from a conductive roller on which the plastic sheet moves, with the fixed electrode being embedded in a coating of glass. FIG. 4 shows an alternative embodiment of the electrode assembly including a metal tube electrode disposed in a glass sleeve and terminating somewhat short of the end of the glass sleeve facing the moving plastic sheet. The electrode assembly is spaced from the moving plastic sheet.
U.S. Pat. No. 4,555,171 to Clouthier et al. illustrates a corona charging electrode including a plurality of metallic filaments. These filaments could have a diameter of approximately 0.001 inch. The device is for use in copying or printing apparatus.
U.S. Pat. No. 4,353,970 to Dryczynski et al. discloses apparatus for charging a dielectric layer. As shown in FIG. 10, the dc voltage electrode could include a number of individual metal wires which are held spaced apart and insulated with respect to one another between a pair of glass plates with each of the electrodes extending toward the layer beyond the plates.
From the above, it is seen that the concept of using corona discharge for the purpose of treating the surface of conductive material is well known and practiced in the art. There remains, however, a need in the art for improved methods and techniques for efficiently applying corona discharge treatments to a wide variety of different shaped and contoured surfaces.